keyboard contact rubber fun

Tim Ressel Tim_R1 at
Thu Aug 24 17:59:05 CEST 2000


There are lots of ways to rig a magnetic sensor. I'm sure a simple and easy one

Two types of hall sensors: ones that act like switches, and ones that give
proportional outputs. The latter are called linear hall sensors.

No, a iron plunger gives a signal proportional to the velocity of the plunger.
An LVDT would give positon info, but those are really complicated to do
one-per-key. Linear Hall is the way to go I think. Gives a DC voltage
proportional to the magnetic field its exposed to. 

As usual, I advocate using a uP for reading all of these sensors.

Tim Ressel--Compliance Engineer
Verifone Division
3755 Atherton Rd.
Rocklin, Cal
timothy_ressel at

-----Original Message-----
From: Jim Patchell [mailto:patchell at]
Sent: Thursday, August 24, 2000 8:19 AM
To: Tony Allgood
Cc: Synth DIY
Subject: Re: keyboard contact rubber fun

    One thing I always wanted to try was using an iron plunger going into an
inductor.  The only thing that stopped me was it seemed like an awful lot of
work, both mechanical and electronic.  But this should be able to give you a
signal that is proportional to how far the key is pressed down.  It has some
very interesting posibilities.

Tony Allgood wrote:

> Sounds a good idea to replace these things... and I have to replace the
> whole set of contacts in a D-50 tomorrow morning.
> But we have to think about velocity too, and aftertouch. The Prophet T-8
> had some sort of opto thing, it worked very well according to some. But
> little magnets and hall effect things could work too. And you could get
> really bizarre glissandos going by rubbing the keyboard up and down with
> a big loudspeaker magnet.

    Now, this idea I like!  It has a lot of posiblities as well.

    Another magnet idea is hall effects sensors.  I think some of these will
also give a signal that is proportional to the where abouts of the magnet,
if I am not mistaken.

> Regards,
> Tony Allgood  Penrith, Cumbria, England
> Modular synth circuits, TB303 clone and Filter Rack
> My music:


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